The persistence of HIV and sexually transmitted infection (STI) epidemics indicate that more powerful and sustainable interventions are needed, particularly for disadvantaged inner-city populations at highest risk and difficult to reach. The proposed study is a randomized, controlled efficacy trial of a theoretically based, peer outreach, network-oriented intervention that targets young adults at risk for HIV in Baltimore. We will assess the efficacy of a peer outreach education intervention to affect network norms and risk behaviors and to sustain risk-reduction behaviors of participants and their peer network members. The control condition will be the small group cognitive behavioral, individual-focused intervention (NIMH Multisite HIV Prevention Trial Group, 1998). The experimental condition will include a network-oriented component that emphasizes a pro-social identity and the super ordinate goals of protecting one's family and community and provides skills training in peer outreach education. Participants will be inner-city young adults, aged 18 to 35 years, recruited from targeted sampling of areas with high rates of HIV. Those randomly assigned to the experimental condition will be trained to conduct peer HIV/STI education and distribute prevention materials among their social networks and others at risk. Outcome evaluation will include pre-test and post-test assessments of 400 index participants (200 per arm) and 800 of their peer network members at visits 3,6,12,18 months following the intervention. The study's main outcome measures will be sexual risk behaviors. Mediating and moderating variables will also be assessed. To cross-validate self-reported behaviors we propose non-invasive laboratory assessment of HIV and STIs. In addition to their health sequelae, STIs are risk factors for HIV infection, are correlates of HIV-related sexual behavior, help validate self-reported sexual risk behavior, and may aid in the understanding of sexual mixing patterns among this group.